1. Field of the Invention
This invention relates to room temperature vulcanizable silicone sealants containing fungicides.
2. Background Information
Silicone compositions which cure to produce elastomers at room temperature are widely used as sealants and caulking materials because they have a unique property profile for applications, such as in building construction. These properties include excellent weatherability, resistance to heat, maintaining their flexibility at low temperatures, ease of application, and rapid cure in place. However, the silicone sealants over a period of time often become dirty or stain the surrounding substrates adjacent to them. This creates an unattractive appearance and cleaning the dirt off the sealant and the stain off the adjacent building materials is expensive and often the results are unsatisfactory. It is therefore the hope of the construction industry to have a silicone sealant developed which does not become dirty or stain the adjacent building materials. Many methods have been proposed to eliminate the problems of dirt pick-up and staining encountered with the use of room temperature vulcanizable (hereinafter referred to as RTV) silicone sealants in construction.
Some of the approaches to overcoming the staining problems and the dirt pick-up problems are the use of surfactants described by Arai in U.S. Pat. No. 4,460,740, issued Jul. 17, 1984, by Inoue et al in U.S. Pat. No. 4,695,603, issued Sep. 22, 1987, and in Japanese Kokai (Laid Open) Patent Publication No. 56-76453, and Japanese Kokai Patent Publication No. 56-76452, both assigned to Toshiba Silicone KK, and published on Jun. 24, 1981.
An especially successful approach to eliminating the dirt pick-up and the staining problems is described by Altes et al in U.S. Pat. No. 5,357,025, issued Oct. 18, 1994. Altes et al describe the use of a siloxaphobic agent which contains per molecule at least one perfluorocarbon group of the formula C.sub.x F.sub.(2x+1) -- where x has an average value of at least 6. Using this siloxaphobic agent in combination with a drying oil results in a particularly useful sealant with good resistance to dirt pick-up and little or no staining of adjacent materials. Altes et al is hereby incorporated by reference to show RTV silicone sealant compositions which provide resistance to dirt-pick-up and staining, especially those which contain a drying oil. The inventors found that when RTV silicone sealants containing drying oil were used, the surface of the cured silicone sealant which had a drying oil oxidation product layer gradually disappeared and its effectiveness for remaining clean was reduced. However, a drying oil surface layer on a sealant exposed to the outside environment often experiences an additional problem, the formation of fungus on its surface which is as much of a problem aesthetically as the dirt pick-up or the staining. One solution to eliminate or at least retard the growth of fungus on the surface of a sealant is to include a fungicide in the formulation. The use of a fungicide can lead to other difficulties. For example, some of the known fungicides can cause other unsatisfactory property changes. Some fungicides are effective, but degrade (chemically altered) when exposed to ultraviolet radiation (hereinafter referred to as UV), become ineffective and can discolor the sealant. Once a sealant is discolored, removal of the discoloration is not practical. It is therefore the desire to overcome these problems.